1. Field of the Invention
The present invention relates to an apparatus for the production of .epsilon.-caprolactam and a process for producing .epsilon.-caprolactam using the apparatus. More precisely, the present invention relates to an apparatus for the production of .epsilon.-caprolactam which is capable of decreasing an amount of unreacted cyclohexanone oxime as an impurity, remaining in the reaction product .epsilon.-caprolactam and capable of increasing the yield of .epsilon.-caprolactam, and a process for producing .epsilon.-caprolactam using such an apparatus.
2. Description of Related Art
.epsilon.-Caprolactam is a key chemical product used as a raw material for Nylon or the like. For the production of .epsilon.-caprolactam, a process has been adopted in which cyclohexanone oxime is subjected to a Beckmann rearrangement reaction using fuming sulfuric acid under liquid phase conditions (liquid phase Beckmann rearrangement process). In addition to that, many variations for the production have been proposed in which cyclohexanone oxime is subjected to a Beckmann rearrangement reaction using a solid catalyst under gaseous phase conditions (gaseous phase Beckmann rearrangement process) [Examples of the catalyst include a boric acid catalyst (JP-A-53-37686, ibid. 46-12125), a silica-alumina catalyst (British Patent No. 881,927), a solid phosphoric acid catalyst (British Patent No. 881,956), a Y-type zeolite catalyst (Journal of Catalysis, 6,247 (1966)), a crystalline aluminosilicate catalyst (JP-A-57-139062) and the like.]
The conventional liquid phase Beckmann rearrangement process using fuming sulfuric acid, which is widely adopted in the industry, had not only problems such that a much amount of sulfuric acid is required but also problems such that a large amount of ammonium sulfate, for example, as much as about 1.7 ton of ammonium sulfate per ton of .epsilon.-caprolactam is produced as the by-product since neutralization of the sulfuric acid with ammonia is necessary for recovering .epsilon.-caprolactam from the reaction product of the Beckmann rearrangement reaction.
On the other hand, the gaseous phase Beckmann rearrangement process using a solid catalyst has advantages such that no ammonium sulfate is produced. However, the gaseous phase Beckmann rearrangement process has a problem such that carbonaceous substances deposit on the solid catalyst during the reaction in the process, resulting in coverage of active sites with the carbonaceous substances, which leads to gradual deactivation of the catalyst. In order to regenerate the deteriorated catalytic activity, a method is proposed in which the carbonaceous substances on the catalyst is oxidized and removed by an oxygen-containing gas. However, this method causes other problems in a fixed bed reaction system such that the production of .epsilon.-caprolactam is interrupted during the regeneration operation for the catalyst, and a switching operation between the production of .epsilon.-caprolactam and the regeneration of the catalyst is troublesome. Another method for the regeneration is also known in which both the gaseous phase Beckmann rearrangement reaction (i.e., the production of .epsilon.-caprolactam) and the regeneration of the catalyst are respectively performed in each fluidized bed system and the operations of the reaction and the regeneration are continuously carried out at the same time by circulating the catalyst through the reactor and the regenerator (for example, JP-A-55-53267).
Although the above described problems have been solved by such a method of fluidized bed system, there are many problems furthermore in the conventional gaseous phase Beckmann rearrangement reaction such that all of cyclohexanone oxime can not be consumed in the reaction. It is unavoidable that some unreacted cyclohexanone oxime remains in the reaction product. However, it is not easy to perform separation of cyclohexanone oxime from .epsilon.-caprolactam by a commonly used distillation procedure. Since, however, a high-purified .epsilon.-caprolactam is needed for producing Nylon or the like, separation byaprocedure such as crystallization, extraction, azeotropic distillation or the like is necessary, while such a procedure is costly and undesirably from the industrial viewpoint. Under such a circumstance, a new process has been desired which decreses the amount of unreacted cyclohexanone oxime as possible in the reaction product in the step of gaseous phase Beckmann rearrangement reaction.
In JP-A-46-3727, it is pointed out that separation of cyclohexanone oxime from .epsilon.-caprolactam by a physical separation method is quite impossible, or too costly if possible, since both compounds have similar physical properties. In order to avoid this problem, a process is disclosed in which a cyclohexanone oxime-containing .epsilon.-caprolactam obtained by the gaseous phase Beckmann rearrangement reaction is treated with sulfur dioxide at a temperature of from 70 to 170.degree. C. In this process, however, a gaseous crude .epsilon.-caprolactam which is formed at an elevated temperature of 300.degree. C. or higher should be cooled to 170.degree. C. or lower to be liquefied before reacting with gaseous sulfur dioxide and, therefore, the procedures thereof are troublesome. In addition, a step for removing sulfur dioxide is also needed.
In JP-A-51-52188, a process is disclosed in which a crude .epsilon.-caprolactam obtained by the gaseous phase Beckmann rearrangement reaction is mixed with an acidic mixture obtained by Beckmann rearrangement of cyclohexanone oxime using fuming sulfuric acid. Although nothing is described in the specification about cyclohexanone oxime remaining in the crude .epsilon.-caprolactam obtained by the gaseous phase Beckmann rearrangement reaction, the cyclohexanone oxime contained as an impurity may be converted to .epsilon.-caprolactam by Beckmann rearrangement with the treatment in a strongly acidic medium. This process, however, is not preferred because ammonium sulfate is produced due to the use of fuming sulfuric acid.